1. Field of the Invention
The invention relates generally to devices for reducing air flow resistance and drag on trucks, semitrailers, railway cars, and other vehicles. More particularly, the invention relates to devices for redirecting air from airstreams passing around a vehicle into low-pressure zones at the rear of the vehicle.
2. Description of the Prior Art
The profitability of long-distance highway cargo transport depends heavily on the cost of fuel, and on the efficiency with which the fuel is utilized. The cost of fuel is largely outside the control of the cargo transporter; however, the efficiency of fuel utilization may be increased. One method involves reducing resistance to forward motion of a vehicle through the air. Resistance to vehicular motion takes two major forms. First, the volume of air immediately in front of the vehicle acts as a barrier. A vehicle is then required to expend energy to push this volume of air aside, thereby reducing fuel economy. Significant advances have been made in aerodynamic design of semitrailer tractors and trailers, including the incorporation of deflectors to redirect air around substantially vertical planar surfaces of vehicles. A commonly used deflector takes the form of a dome-shaped device mounted on the top of a semitrailer tractor cab; the dome deflects air upward toward the top of the trailer, rather than allowing the air to flow directly against the vertical front of the trailer. Resistance to forward motion of the vehicle from the body of air in front of the vehicle is reduced. A measurable increase in the efficiency of fuel utilization, and a concomitant increase in mileage traveled per gallon of fuel used (fuel mileage), is obtained.
A second, and at least equally pernicious, form of resistance to a vehicle in motion lies in the drag on the vehicle caused by the formation of reduced-pressure zones at the rear of the vehicle, or in between units of a combination vehicle, such as a string of multiple trailers. The airstreams passing over the top and along the sides of the vehicle recombine behind of the vehicle. However, due to turbulence caused by the passage of the vehicle, a space filled with low pressure air forms between the rear of the vehicle and the point at which these airstreams fully recombine. This zone of turbulent low-pressure air acts as a partial vacuum, and induces drag on the vehicle in a backward direction. The work that must be performed by the engine to pull the vehicle forward is then increased, thereby decreasing fuel mileage.
Vehicular drag has long been recognized in the art, and a number of solutions have been proposed. One common solution lies in streamlining the rear of a trailer. Airstreams passing along the trailer flow together more smoothly, with reduced turbulence. A smaller low-pressure zone is produced at the rear of the vehicle, with a marked reduction in drag. However, a number of legacy trailers exist; which would require a sizable expense to replace. Accordingly, methods of reducing drag which may be easily and inexpensively retrofitted onto existing trailers would be attractive to trucking companies.
One method of retrofitting existing trailers with streamlined drag-reduction devices lies in the use of conical or pyramidal devices or airfoils on the rear of a trailer. Such airfoils act in the same manner as the streamlined rear of a trailer as described above, in that the airfoils allow airstreams to flow together more smoothly. An advantage over the above streamlined trailers is that airfoils may be readily retrofitted onto an existing, non-streamlined, trailer. However, these devices do have certain drawbacks. When used with trailer trucks, airfoils normally fit over the doors at the rear of the trailer. Thus, these devices may not be simply mounted on a trailer and left in place. Instead, these devices must be assembled and mounted on the rear of the trailer after completion of the loading process. Similarly, such devices must be disassembled and removed from the trailer before unloading can begin, causing inconvenient delays in the unloading and loading processes. More importantly, at least some of the savings from increases in fuel mileage or fuel economy may be offset by increased hourly costs for labor. Another drawback of using rear-mounted airfoils on trailers is that the airfoils add significantly to the length of a trailer, making it difficult to use these airfoils to reduce drag in between a pair of trailers mounted in series.
Some airfoil designs allow the airfoils to slide into or out of tracks mounted on the side of the vehicle; while the use of such tracks accelerates the process of positioning airfoils after loading and unloading the trailer, the cost and complexity of retrofitting an existing trailer with a streamlined airfoil is significantly increased.
A second method of retrofitting trailers with a drag-reducing device lies in fitting vanes to the rear corners of the trailers. Corner vanes redirect airstreams passing along the sides of the vehicle to induce flow into a low-pressure zone behind the trailer, thereby reducing the magnitude of the partial vacuum behind the trailer, and hence reducing the drag on the vehicle. If two trailers are connected in series, formation of a low pressure zone between the trailers may be prevented by mounting vanes to the rear of the front trailer, such that air flowing along a front trailer is redirected into the space between the front trailer and rear trailer.
Many vanes of the prior art are rigidly mounted to the rear corners of a trailer. While these do an effective job of preventing drag, they do impede opening the doors on the rear of the trailer. Many trailers are designed with doors that open so as to lie flat against the side of the trailer, so as to allow the trailer to be loaded or unloaded in a small or enclosed space. However, the vanes, when rigidly mounted to the trailer, prevent the doors from opening completely. The inability to fully open the vehicle doors is an inconvenience during the loading/unloading process.
It is an object of the invention to provide an apparatus that will increase fuel efficiency of powered vehicles towing unpowered vehicles having a generally planar rear surface by reducing drag on the unpowered vehicles.
Another object of the invention is to provide an apparatus that may be retrofitted onto existing vehicles so as to reduce drag, without requiring that the apparatus be dismounted or remounted at any point during the unloading/reloading process.
In another object of the invention, the drag-reducing apparatus may be retrofitted onto existing vehicles without impeding the normal uses of the vehicles. These normal functions include, but are not limited to, the ability to fully open the doors of the vehicles during loading/unloading; and the ability to connect multiple vehicles in series.
It is an additional object of the invention to provide an apparatus that will reduce drag on vehicles having a generally planar rear surface, including trailers and railway cars.
It is a further object to provide an apparatus that will reduce drag on vehicles, where the device may be readily retrofitted onto existing vehicles.
The foregoing objects and advantages of the invention are illustrative of those that can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus, these and other objects and advantages of the invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variation which may be apparent to those skilled in the art. Accordingly, the present invention resides in the novel methods, arrangements, combinations and improvements herein shown and described.